Wooden Roof Framing

Most roof framing uses lumber.Wooden roof frames are strong, lightweight, and easy to construct. Your local building code will contain span charts specifying the lumber dimensions that meet your design requirements. It's a good idea to take a look at these span charts early in your design process, since they can help you decide on overall roof dimensions.You don't want to plan a roof that is prohibitively difficult or expensive to frame.

There are several ways to go about framing a wooden roof system:

• Site framing with dimensional lumber. Using the span charts in your building code, you can cut the rafters, joists, and collar ties required by the design of your roof and use the appropriate connections and fasteners to assemble the roof.

• Manufactured roof truss systems. Manufactured trusses are engineered to use small-dimension lumber — 2-by-4 and 2-by-6-inch — to meet the load requirements specified for your region.They are engineered to fit your plans, are factory built and assembled, and delivered to your site. Their cost is often equal to, or lower than, the cost of the heavier lumber you'll need if you frame the roof yourself. The truss company employs an engineer to design the trusses, so prices include the cost of having an engineer stamp your roof plan. If you are paying a carpenter for framing, manufactured trusses are likely to be a cheaper option. For complicated roofs, a combination of manufactured trusses and site framing may be optimal. Building inspectors often prefer manufactured trusses over site-framed roofs, especially if the builder is a first-timer. Environmentally, the small-dimension lumber used for manufactured trusses can be more sustainably harvested than the heavier lumber used for traditional framing.

• Wooden I-beams. Manufactured wooden I-beams can be used to site-frame a roof with spans that would have made regular-dimensional lumber prohibitively large and costly to the environment. The wooden I-beams use a glued, oriented strand board (OSB) to create a deep, thin beam with small-dimension lumber on top and bottom as stabilizers. Lighter and less prone to warping and cracking than dimensional lumber, they can prove easier to work with. The costs are comparable to the dimensional lumber they replace.

• Timber framing. A timber-framed roof uses very large-dimensional lumber with traditional notched joinery to create a strong and beautiful roof frame. Although usually part of an entire timber-frame shell, it is quite possible to have a timber-framed roof only. Sheathed and insulated on the outside of the timbers, the exposed woodwork is left visible inside the building.

• Mandala framing. Mandala roofs (also called the reciprocal-frame roof structure),use large-dimensional round or squared timbers arranged in a circular pattern, and designed such that each member rests on its neighbor in a self-supporting system to create roofs that are typically used to cover round buildings, but can also be adapted for square or multi-sided structures.

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